Houch,
The expenses you refer to come under the heading of Flat Rated Expenses, and yes, they are negotiated at a regional tax office level.
Give your employers tax office a ring (quoting your employers tax code) and they will let you know the figure that has been agreed, then just include in your tax return.
Unfortunately the amounts can vary by £100's of pounds between the various offices. Mine by way of illustration is £580, many are less, some probably more.
Edited because I forgot to say that as yet nobody has asked for any receipts, which is good, because I aint got any.
[ 11 August 2001: Message edited by: Super Stall ]